Explosion bonded aluminum to steel

ABSTRACT

Composite products of certain aluminum and steel layers metallurgically bonded together over at least 90 percent of their interface by a substantially diffusionless wavy bond containing, by area, at least about 70 percent direct aluminum-to-steel bonding are prepared by an improved explosion-bonding process wherein at least one layer of aluminum is caused to collide progressively with a layer of steel at a velocity of about from 2,500 to 3,400 meters/sec. and at an impact angle of about from 14* to 25*, the opposed surfaces of said layers being disposed at an angle of less than 5* prior to detonation of said explosive.

EXPLOSION BONDED ALUMINUM T0 STEEL Inventors: William F. Sharp, in, Bellmawr;

Thomas F. Enrlght, Woodbury Heights, both of NJ.

Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

Filed: Feb. 11, 1971 Appl. No.: 114,662

Related US. Application Data Continuation-impart of Ser. No. 695,506, Jan. 3,

1968, abandoned and is a division of Ser. No. 756,704, July 30, 1968, Pat. No. 3,583,062.

References Cited UNITED STATES PATENTS 4/1970 Chudzik 29/486 Mar. 19, 1974 3.137.937 6/1964 Cowan et al..;. 29/486 3,194,643 7/1965 Ma et a1 29/4701 X 3,238,071 3/1966 Holtzmann etal. 29/486 X 3,397,045 8/1968 Winter 29/194 X 3.397.444 8/1968 Bergmann et a1... 29/4701 3.233.312 2/1966 Cowan et a1 29/194 Primary Examiner-J. Spencer Overholser Assistant Examiner-Ronald 1. Shore [57] ABSTRACT Composite products of certain aluminum and steel layers metallurgically bonded together over at least 90 percent of their interface by a substantially diffusionless wavy bond containing, by area, at least about 70 percent direct aluminum-to-steel bonding are prepared by an improved explosion-bonding process wherein at least one layer of aluminum is caused to collide progressively with a layer of steel at a velocity of about from 2,500 to 3,400 meters/sec. and at an impact angle of about from 14 to 25, the opposed surfaces of said layers being disposed at an angle of less than 5 prior to detonation of said explosive,

4 Claims, 3 Drawing Figures l EXPLOSION ESQNEED ALUMINUM TO STEEL CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our prior copending application Ser. No. 695,506, filed Jan. 3, 1968 now abandoned and is a division of Application Ser. No. 756,704, filed on July 30, 1968, now US. Pat. No. 3,583,062.

BACKGROUND OF THE INVENTION US. Pat. Nos. 3,137,937 and 3,264,731 describe at the bond'zone, hence improved strength and ductilprocesses for producing 'metallurgically bonded clad products by means of explosives. According to the processes described, the metal layers to be metallurgically bonded are propelled'together with an explosive so as to cause them to collide progressively at a velocity which is below 120 percent, and preferably below 100 percent, of the sonic velocity of the metal in the cladding system having the highest sonic velocity. The

, metal layers initially are spaced from each other at an angle, usually less than 40, and preferably about (i.e., they are substantially parallel) and a layer of detonating explosive is positioned adjacent the outer surface of at least one of the layers and then initiated so as to cause the required progressive collision.

Three types of bond zones, each completely metallurgical, may result from the above processes: direct metal-to-metal, uniform melted layer, or a mixture of these arranged in a wave pattern. Direct metal-tometal" means that the metals are bonded together at their adjoining surfaces to form an interface without the intervention of a layer of solidified melt therebetween. The uniform melted layer type of bond zone is that in which the metals are bonded together via anv intervening layer of solidified melt of substantially homogeneous composition, forming substantially two interfaces. As seen in a cross-sectional view taken normal to the interface and parallel to the direction of detonation, the wave pattern type of bond zone is composed of periodically spaced discrete regions of solidified melt between areas of direct metal-to-metal bond. This means that at the bond zone there is one interface, i.e.,

metal-to-metal, in the areas where the bonding is of the direct metal-to-metal type, and two interfaces, i.e., metal-melt and melt-metal, where melt pockets or regions are present. Regardless of the type of bond zone, there is substantially no diffusion across any interface at the bond zone in the as-bonded product.

Irrespective of the metals being bonded, the melted layer type of bond produces a product of high shear strength; and in metal systems which form ductile alloys, this type of bond gives a product also capable of being worked extensively. However, when brittle alloys or intermetallics are formed, a melted layer bond should be extremely thin (e. g., less than microns and preferably less than one micron) if the. product is to have the workability required by forming operations, and even then the cladding or prime .metal layer must be relatively thin, e.g., less than about one-eighth inch. Consequently, as a rule, a high degree of direct metalto-metal bonding with melt regions isolated from each other is preferred in metal systems which form brittle alloys or brittle intermetallic compounds. This is one reason why the wavy bond zone with a major proportion of the bonding consisting of the direct metal-to metal type of bond is preferred. The wavy bond zone ity. According to this explosion-bonding process, the metal layers are initially spaced from each other at an angle less'than 10, and preferably at about 0, and then caused to progressively collide at a certain impact angle and a velocity below that at which large amounts of solidified melt are produced at the interface, impact angles up to about and collision velocities of about from 1,400 to 2,500 meters/sec. being exemplified. The products thus produced, including those wherein aluminum is bonded to steel, are bonded over at least percent of each interface and have low melt content. it

has been found, however, that the commercially important system, aluminum/steel, is unlike the other dissimilar metal combinations in two respects. First, in the usual situation where aluminum is driven into the layer of steel, decreasing collision velocity within the exemplified range of about from 2,500 to 1,400 meters/sec. does not increase the amount of direct aluminum-tosteel bond at impact angles up to about 20. Second,

the preferred wavy type bond wherein any interfacial when the aluminum is caused to collide with the steel at such impact angles.

Aluminum/steel clads are acquiring increased technical importance for use as transition joints in structural and electrical systems. Aluminum/steel structural transition joints, .e.g., for marine and aerospace applications, must have high tensile strength and a high degree of ductility. in electrical transition joints, the highest possible conductivityv across the aluminum/steel bond is desirable. Since aluminumand steel form intermetallic compounds which are brittle andoffer substantially more resistance to the passage of electricity than direct aluminum-to-steel bond, it is readily seen that there is need for aluminum/steel clads wherein the bond has not only a low melt content but also a high percentage of direct aluminum-to steel bond.

SUMMARY OF THE ENVENTION This invention provides an improvement in aluminum/steel composites wherein at least one layer of alu minum whose yield strength before bonding is up to about 17,000 psi and a layer of steel having a yield do not exhibit the gradient composition characteristic of diffusion-bonded products. Preferably, the as- .aluminum layer whose yield strength is up to about 17,000 p.s.i. with a layer of steel whose yield strength in the normalized condition is up to about60,000 psi, at a collision velocity of about from 2,500 to 3,400 meters/sec. and an impact angle of about from 14 to 25, 1

the opposed surfaces of said layers being disposed at an angle of less than 5 prior to detonation of the explosive.

The collision velocity is the velocity with which the line or region of collision travels along the steel and aluminum layers to be bonded. The impact angle is the angle between the steel and aluminum layers on collision.

The term aluminum" as used herein with reference to the metal layer bonded directly to the steel layer denotes pure aluminum as well as aluminum-base alloys containing at least 85 percent aluminum, by weight.

Unless otherwise specifically indicated, the term "steel" is used herein to denote carbon steel and lowalloy steels, i.e., alloy steels that contain less than about 5 percent alloying elements, by weight.

DESCRIPTION OF THE DRAWINGS FIGS. 2 and 2A are photomicrographs at two different magnifications of a typical wavy bond zone ,obtained in aluminum/steel clads made by the process of this invention.

DETAILED DESCRIPTION OF THE INVENTION According to the present process, a layer of aluminum having a yield strength of up to about 17,000 psi is metallurgically bonded to a layer of steelwhose yield strength in the normalized condition is up to about 60,000 psi by explosively propelling the aluminum layer toward the steel layer so as to cause the aluminum and steel layers to collide progressively at a velocity of about from 2.500 to 3,400 meters per second and an impact angle of about from 14 to 25. Carrying out the explosion bonding process in this particular collision velocity range at the specified impact angles and with the designated types of aluminum and steel produces at least 90 percent bonding by a substantially difi'usionless wavy bond zone in which at least about 70 percent of the bonding is of the direct metal-to-metal type, i.e., at least about 70 percent of the bond area is a metal-tometal interface,: as contrasted to metal-to-solidified melt interfaces. By virtue of their high'percentage of direct aluminum-to-steel bonding, the products of this invention exhibit a ductile type of failure in both shear and tension, and high resistance to shock loading as evidenced by the fact that they cannot be separated at the interface by a chisel. Hence, these products are capable of being worked extensively without failure at the bond zone.

The manner in which the, nature of the bonding varies with collision velocity in aluminum/steel explosion clads can be understood more clearly by reference to FIG. lJThe plot in FIG. 1 is representative of the results obtained when a 0.5-inch-thicl't layer of ll00-F aluminum is clad explosively to a LS-inch-thick layer of AlSl-SAE-IOOS steel. the metal layers initially being disposed substantially parallel to each other and with the standoff between them and the explosive load being such that'a steady-state impact angle of about l8-20 is set up between the layers during bonding. In FIG. 1, the curve shown is drawn through points obtained by plotting collision velocity, i.e., detonation velocity of the explosive since the metal layers initially are substantially parallel, as the abscissa and percent direct metal-to-metal bonding obtained as the ordinate. Just at about 2,500 meters per second, there is an abrupt rise in percent metal-to-metal bonding, associated with a transition from a substantially straight or irregular bond zone to a distinct wavy pattern. A bond zone characteristically obtained at about this velocity is shown in FIG. -2 which is a cross-sectional view (6.6x) normal to. the surfaces of the clad composite and parallel to the direction of detonation travel, from right to left. FIG. 2A is a magnification of the boxed-in area of FIG. 2. The interface is the continuous wavy line between the aluminum layer (top) and steel layerlbottom). Asbest seen in FIG. 2A, a normal drawn through most points on the interface passes only through aluminum and steel, i.e., the bonding is metal-to-metal. At a few points, normals pass through aluminum, solidified melt and steeLI-Iere the bonding is via the melt layer. A region of solidified melt is completely encapsulated by the overlapping steel layer and is not present at the interface. The percent metal-to-metal bonding defined herein is obtained by measuring the total length of the continuous wavy interface, and the lengths of the small sections of the interface which are aluminum/melt interfaces. The difference between the total length of the wavy interface and the sum of these section lengths, divided by the total length of the interface gives the percent metal-to-metal bonding.

The minimum collision velocity for wave formation increases slightly as impact angle decreases, i.e., the dotted transition line of FIG. 1 shifts to the right when the impact angle is reduced to below about l8-20. As a rule, the minimum velocity for wave formation increases substantially linearly from about-2,500 to about 2,900 m./sec. as the impact angle decreases from about 20 to about I4.'\Vhatever impact angle is chosen, the

lation is complete, and there may be no melt'at the interface, e.g., the melt will not be observable at a magnification of 1,000X. As the collision velocity is inincreases so does the rate of melt formation with increasing collision velocity.

The collision velocity range of about from 2,500 to 3400 in/sec. is employed for the aluminum/steel systems of this invention because it gives a high percentage of directaluminum-to-steel bonding. This'affords the best bond ductility. Also, since direct aluminum-tosteel bonding has substantially no measurable electrical resistance, it is important where the clad composites are to be employed in electrical systems, e.g., as transition joints. Whether strength or conductivity is the prime consideration, bonds containing at least about 90 percent direct aluminum-to-steel bonding are most desirable, and for this reason, the collision velocity preferably will not be far above the transition velocity for wave formation. For example, where this transition velocity is about 2,500 m.sec., the collision velocity preferably will not exceed about 2,900 m./sec. To ensure wave formation, the explosive preferably will be chosen so that the calculated collision velocity is at least about 100 meters/sec. higher than this transition velocity, thus making the preferred minimum velocity at least about 2,600 m/sec. J

Within the collision velocity region'specified above, the aluminum and steel layers should collide at an im pact angle sufficient to cause wave formation but not less than about 14. Below this value, wave formation is difficult to obtain irrespective of the collision velocity employed. For a given thickness of the aluminum layer, the impact angle produced increases with increasing explosive loading, and increases with increasing initial standoff or angle to a maximum-Stated differently, impact angle increases with the aluminum displacement velocity and reaches a maximum with stand off. The maximum impact angle that will be employed is governed partly by the size of the waves desired, wave size increasing with increasing impact angle. Therefore, the maximum impact angle which should be used is the angle above which the amplitude of the waves formed is larger than desired. In addition, since wave size increases also with increasing collision velocity within the velocity range employed in the present process, for a fixed maximum desired wave size, the maximum impact angle which should be used decreases with increasing collision velocity. In any event, the im-, pact angle should not exceed about 25 since higher an gles often result in pronounced edge effects and irregular bond patterns, and tend to give melt regions of sufficient volume that they will have a significantly deleterious effect on bond strength, often because of solidification (voids) caused by shrinkage of the melt upon cooling. Best results are obtained when the steady state impact angle is about from 14 to lmpact angles can be measured from framing camera sequences using a reflected grid-displacement technique. Such a technique is described by WA. Allen and CL. McCrary in Review of Scientific Instruments, Vol. 24, pages 165-171 (1953).

In general, to achieve the impact angles useful in the present process in the preferred parallel arrangement,

an explosive loading weight of about 0.2 to 3 times the weight of the layer(s) to be driven is used, while a standoff of about from 1 to 6 times the driven layers or layers thickness is employed. Explosive loading weight is the weight per unit area of explosive material, exclusive of any non-explosive ingredients which may be present in a given explosive composition.

Aluminum may be clad to one side of a steel layer,

or to both sides. Two outside aluminum layers may be 4 clad onto the steel in two stages, or they can' be propelled simultaneously toward the steel layer. Each aluminum layer that is to be bonded directly to the layer of steel is pure aluminum or an aluminum-base alloy containing at least 85 percent aluminum, by weight, and has a yield strength, measured before bonding, i.e., when the aluminum layer is ready for bonding, that does not exceed about 17,000 psi. When an aluminumbase alloy is employed, the type of alloying elements is not critical however, aluminums containing less than 2.1 percent magnesium plus silicon, by weight, are preferred. Also, the aluminum layer( s) bonded to steel in the present process may be in the fully annealed, partially annealed or hardened condition, the important consideration being their yield strength just before bonding. Exemplary aluminums are those having the designations 1,l00-F, 3003-0, 5005-0, 5457-0 and 6061-0 (Aluminum Association numbers and temper designations). After bonding, i.e., in the as-bonded condition, the yield strength of the aluminum will be substantially higher than before bonding, primarily because of substantial work hardening at and adjacent the bond zone. Often, and particularly when the aluminum is at least about one-quarter inch thick, at least the outside surface of the aluminum layer will have a yield strength of about 17,000 psi. or less. This yield strength is conveniently computed from Brinell hardness measurements taken on the aluminurns outside surface.

The yield strength of the steel layer, measured when it is in the normalized condition and before'bonding, will not exceed about 60,000 psi. This layer will be carbon steel or low-alloy steel containing less than about 5% alloying elements by weight. The type of alloying elements is immaterial, the only requirement being that their quantity and the yield strength of the steel layer be within the above limits. The steel layer may be in the normalized or annealed condition at the time of cladding, but preferably is normalized. Suitable steels include those having the ASTM designations A-212-B (A-fil-GRSS to and A204, and those having the SAE designations 1008 and 4620. As bonded, the actual yield strength of the steel layer will be substantially the same as that of the starting layer because work hardening is slight and is confined to a very narrow layer of steel, e.g., about 50 to 70 mils thick, at the bond zone. in the normalized condition, the products steel layer will have a yield strength of up to about 60,000 psi. v

For two-layered products, the aluminum and steel layers to be bonded generally are at least about 0.125 inch thick, the bonding of thinner layers being feasible but not often in demand. For most applications, the

steel layer will be at least about 0.5 inch thiclt. Also, as

and composition. a wavy bond is difficult to form, and if formed, will contain too much solidified melt. The exact reason for this is unknown, but it is believed that the metals resistance to wave formation causes heat generation, hence an increasing amount of melt when the limitations on amount of alloying elements and yield strength are exceeded. It is to be understood that these limitations apply to the steel and aluminum layers that are to be bonded directly to each other, and not to layers of. different metals that may be bonded to the outside surface of the aluminum and/or steel layer. For

example, one side of the steel layer can be bonded to a layer of aluminum meeting the above requirements while the other side of the steel'layer is bonded to a layer of high-alloy steel, e. g., stainless steel; or, one side of the aluminum layer can be bonded to a layer of carbon or low-alloy steel, as defined above, and the other side to a layer of aluminum-base alloy whose yield strength exceeds about 17,000 psi. In such cases,-the three metal layers can be bonded together simultaneously, or any pair can be bonded first and athird subsequently bonded to the vproper surface of the twolayered composite.

An additional requirement for wavy bond formation according to the process of this invention is that each aluminum layer which is to be bonded directlyto the layer of steel be caused to progressively collide with the layer of steel. In other words, each such aluminum layer is explosively driven, either directly by the explosive itself or indirectly by means of an explosively propelled metal layer. This procedure notonly gives the above-described low-melt-content wavy bonds at the collision velocities employed in;the process of this invention, but usuallyalso requires the least amount of explosive to obtain proper bonding conditions, since the mass of the aluminum layer per unit area normally is substantially less than that of the steel layer..Although the layer of steel can be driven, if desir'edyit is more practical to support thesteel layer and explo sively propel only the aluminum layer(s).

The metal layers can be arrayed initially parallel to, and spaced apart from, each other, or at an angle less than. Higher angles are operable but normally give non-uniform bonds when commercial size metal layers are being clad. EThC substantially parallel arrangement is preferred, however, for reasons of easier operability and greater uniformity of the bond zone produced. A layer of detonating explosive is placed adjacent the metal layer(s) to be driven, and is initiated so that detonation is propagated substantially parallel to the surface of the adjacent metal layer. It the metal layers are initially parallel, the collision velocity equals the detonation velocity of the explosive, and an explosive having a detonation velocity in the range of about from 2,500 to 3,400 meters/sec. is employed. When the angle cladding technique is employed, explosives having higher detonation velocities can be used, since the required collision velocity can be achieved with explo sives of higher detonation velocity by increasing initial angle and/or explosive load.

Typical explosive compositions useful in the present process are described in the aformentioned copending US. Pat. application Ser. No. 503,261, the disclosures of which are incorporated herein by reference. ltis preferred to have the layer of explosive overhang each edge of the adjacent metal layer by a distance .at least equal to twice, and usually less than about 4.5 times,

the latter layer's thickness. This procedure substantially eliminates non-bonding at the edges, hence insures the maximum degree of bonding. It is particularly preferred to additionally employ edge-extension pieces on all edges of the aluminum layer to minimize thinning of its edges. These extension pieces should be of the same density and thickness as the aluminum layer and have a width about equal :to the distance the explosive overhangs the driven layer.

The technique employed to initiate the explosive layer(s), support the cladding assembly, prepare the metal surfaces, and otherwise efiect the bonding process are described in the aforementioned patents, the disclosures of which are incorporated herein by reference. Effective means of maintaining the standofi'. distance are described in US. Pat. No. 3,205,574 and copending U.S..Pat. application Ser. No. 587,299, now US. Pat. No. 3,360,848. Also. as in=the processes described in the aforementioned patents and patent applications, the present process can be used to bond aluminum and steel layers of any shape, e.g., planar or tubular, thus to produce aluminum/steelclad products in such forms as plates, sheets, strip, rods, bars, tubing, etc. Clad composites wherein the layers have an interfacial area of at least about one square foot, and particularly planar products, are preferred commercially.

The aluminum/steel composites of this invention are useful as transition joints in structural and electrical systems in which aluminum components need to be joined to steel components; The use of such joints overcomes the problem of brittle intermetallic formation encountered in the fusion welding of aluminum to steel, since aluminum components of the system are welded to the aluminum portion of the transition joints and the steel components to the steel portion. Two-layered composites in which an aluminum layer having a yield strengthtbefore bonding) of less than 17,000 psi is bonded to a carbon or low-alloy steel, e.g., 1,100 or 5,005 aluminum to 1008 steel or A-5l6-GR55, are suitabletransition joints in certain electrical and structural applications. In systems in which the aluminum portion of the transition joint is to be welded'to a component made of an aluminum alloy having a yield strength greater than 17,000 psi, it may be desirable, to assure maximum weld strength, to employ a threelayered transition joint in which a high-strength aluminum alloy, e.g., a high-strength alloy of the 5,000 series such as 5456 or 5083 aluminum, is bonded to the aluminum layer of the two layered composite. ln such cases, one may alternatively use a higher yield strength aluminum of this invention, e.g., 5454 or 5086, as the v outer layer and a preferred aluminum, e.g., 1,100-0 or F, as the interlayer. Transition joints in which a layer of different metal, e.g., stainless steel, is bonded to the steel layer of the two-layered composite, with or without a layer of different metal bonded to the aluminum layer, also are feasible.

A three-layered composite can be produced by explosion-bonding the three layers simultaneously under the conditions defined above, e.g., by positioning the layers at the selected initial standoff from each other and initiating a layer of explosive on the outside surface of the outermost aluminum layer. Alternatively, two layers can be bonded in one step. and the third bonded to the two-layered product in a second step. For example. to. produce acomposite in which an aluminum layer is sandwiched between a steel layer and a layer of higher-strength aluminum. the lower-strength aluminum can be bonded to the steel first under the conditions defined above, and the higher-strength aluminum bonded to the aluminum side of the resulting composite aluminum layer, and the layer of explosive covers both the aluminum layer and the extension pieces. The explosive composition is a granular mixture of 80/20 amatol (80 percent ammonium nitrate/20 percent trinitrounder conditions falling within a broader range than toluene) and 35 to 55 percent sodium chloride based that described for aluminum/steel bonding, e.g., the on the total weight of the composition, the percentage conditions described in US. Pat. No. 3,137,937. A colof sodium chloride being adjusted within this range to lision velocity range of about from 1,800 to 3,200, megive the designated collision velocities. The description ters per second is preferred for the latter step, however, of the metals, standoff, explosive loading, collision veto prevent the formation of solidification defects asso- -l0 l i y. an impact angle employed. and the nature of ciated with the formation of large amounts of melt at tha bond Obtained are Ell/eh in the following table- The the bond zone. In another embodiment, the two 'alumiyield Strengths given for the aluminum and steel layers num layers are bonded together first by any suitable are their actual Yield Strengths bonding- The th d, l i -b di or lpb di d steel layers are in the normalized condition and the aluthen the surface of the lower-strength aluminum is mlhul'h layers have the temper indicated y their bonded to the steel surface. The thicknesses of the lay- Association desighatiohs- All Products are ers can be as desired provided the aluminum layer bonded Over more-than 90 P of the aluminumwhich is bonded to the steel is at least about 0.03-inch Steel lhlel'fatiei cam")! be Separated at the bond Zone by thick to assure well-defined waves. a chisel, and exhibit a ductile type of failure. Their The composites can be used as transition joints in any nds ha e Shear and tensile strengths above those of required manner. As electrical transition joints, for exthe Weaker Parent e al before Cladding- Measureample. they may be employed in aluminum reduction ments of electrical resistance on bars cut from the clad cells, e.g., between aluminum bus bars and steel cathproducts show that substantially no resistance is conode rods. A typical mode of use as structural transition tributed by the bond zone. joints in ship construction, for example, is in joining an The same type anddegree of bonding is obtained aluminum superstructure to a steel deck, e.g., by weldwhen each of Examples 1 to 7 is repeated using the tabing the steel side of the joint to a steel coaming which ulated conditions, but with'the aluminum layer at an is welded to the steel deck, and the aluminum side to angle of about 2 to the steel backer and separated the aluminum superstructure. Transition joints also can therefrom at the closest point by a space equal tothe be employed to join steel deck fittings, e.g. bitts, to an exemplified standoff. A150,. three-layered aluminum/- aluminum deck. In railroad tank car structures, the steel/aluminum composites having the same type and transition joints may be used to join an aluminum tank degree of bonding are obtained by vertically arranging to a steel chassis. v the steel layer and two of the aluminum layers with the The following examples serve to illustrate specific steel layer in the middle, using an additional layer of embodiments of the process and products of this inventhe same explosive, i.e. adjacent the outside surface of tion. However, they will be understood to be illustrative the secondaluminum layer, and simultaneously initiatonly and not as limiting the invention in any manner. ing the explosive layers at corresponding locations, The collision velocity given in the measured detonawhen the conditions are otherwise the same as those tion velocity of the explosive. The percent metal-toillustrated in the foregoing examples.

Aluminum prime metal Steel backer metal Explo- Percent v sive direct Thick- Yield Thick- Yield loading Collision Impact Type ol aluminumness strength has strength Stand- Obi/sq velocity. angle, bond steel (in.) (p.s.i) Type (in) (p.s.i.) oil (in.) (m./sec.) degrees zone bonding 0.5 12,000 c 1008 1.5 32,000 1.5 15, 2,520 18 Wavy-.- 93 1.0 12,000 c 1008 1.5 32,000 2.25 24 2,050 15 .d0 08 0.5 s, 000 c 1008- 1.5 32,000 1.5 15 2,710 10 .00.-.. 04 0.5 17,000 o 1000 1.5 32,000 2.0 12 2,850 17.5 do 02 0.1ss 17,000 A212B" 6.0 49,000 1.0 9 3,020 17.5 0 85 0.5 0,000 01003 1.5 32,000 1.5 15 3,100 15 0-... 77 1.0 12,000 o 1008 1.5 32,000 2.5 21 3,300 10.2 .do 75 Includes weight of the sodium chloride. A-5l6-Grad0 70.

metal bonding is determined as described above with EXAMPLE 8 reference to FIGS. 2 and 2A.

EXAMPLES l-7 An 18 X 24 inch aluminum plate is clad to a supported l8 X 24 inch steel backer plate by positioning the aluminum plate over the backer with facing (opposed) surfaces parallel to each other at a standoff, positioning a layer of explosive on the outer aluminum surface. and point-initiating the explosive at the center of the short edge. In each example, edge-extension pieces of the same composition and thickness as the aluminum layer and having a width equal to four times its thickness are taclowelded to all four edges of the a. A 16 X 32 inch IlOO-HM aluminum plate 0.25 I inch thick is clad to an ASTM A-S l-GRSS steel plate (yield strength 38,000 psi) measuring 16 X 32 inch and having a thickness of 0.5 inch, by the procedure described in Examples l-7. Collision velocity is 3,060 meters per second, and impact angle is 19. The composite produced is bonded over more than 90 percent of the interface by a wavy bond, the direct aluminumsteel bonding being about percent. The product cannot be separated at the bond zone by a chisel, and exhibits a ductile type of failure. The shear and tensile strengths of the bonds are above those of the aluminum before bonding.

b. A 16 X 32 inch 5456-H32l aluminum plate (yield strength 37,000 psi) 0.25 inch thick is clad to the aluminum layer of the composite formed as described in Step (a) above, using the same procedure. The collision velocity is 2,230 meters per second and impact angle l2. The aluminum layers are, bonded over more than 90 percent of the interface by a wavy bond, which is ductile.

The three-layered composite from Step (b), as well as a two-layered composite of 0.5 inch aluminum bonded to 0.5 inch steel, prepared as described above in Step (a), are employed as transition joints in a structure simulating .shipboard construction, steel being welded to steel and aluminum to aluminum without adverse effect on the bond zone.

We claim:

1. A three-layered explosion-bonded composite comprising a layer of aluminum whose yield strength before bonding is up to about 17,000 psi sandwiched between and metallurgically bonded to two metal layers over at least 90 percent of each interface therebetween, one of said metal layers being a layer of aluminum whose. yield strength before bonding is above 17,000 psi, and the other of said metal layers being a layer of steel having con, by weight.

3. A transition-joint assembly comprising an aluminum structuralcomponent, a steel structural component, and a composite of claim 1, said aluminum component being welded to said composite's layer of aluminum whose yield strength before bonding is above l7,000 psi, and said steel component being welded to the, layer of steel of said composite.

4. An assembly of claim 3 wherein said aluminum and said steel structural components are components of a ship.

i t i i i 

2. An explosion-bonded composite of claim 1 wherein the layers have an interfacial area of at least 1 square foot, and the aluminum layer bonded directly to steel contains less than 2.1 percent magnesium plus silicon, by weight.
 3. A transition-joint assembly comprising an aluminum structural component, a steel structural component, and a composite of claim 1, said aluminum component being welded to said composite''s layer of aluminum whose yield strength before bonding is above 17,000 psi, and said steel component being welded to the layer of steel of said composite.
 4. An assembly of claim 3 wherein said aluminum and said steel structural components are components of a ship. 